1. Field of the Invention
The present invention relates to end sealing and impact protection of double-walled pipe bodies and to the method for effecting sealing and providing impact resistance to pipe ends. More particularly, this invention relates to providing sealing and impact resistance to the ends of double-walled pipe having helical ribs between the inner and outer pipe walls.
2. Description of the Prior Art
It is known to employ plastic pipes and fittings in the design and construction of underground conduit systems for conveyance, water and drainage purposes. Individual sections of plastic pipe are joined together in end to end juxtaposition using the so-called "bell and spigot joint" where one end of a pipe or fitting is enlarged or "belled" to receive therein the unenlarged or "spigot" end of an adjacent length of pipe. The inside diameter of the belled section or hub is formed sufficiently large to receive the spigot end of the next adjacent section of pipe with sufficient annular clearance to provide for gaskets or other devices which are designed to prevent leakage at the pipe joints when the pipe sections are joined into a pipe line.
In the past, such plastic pipe has been extruded into various lengths and diameters depending upon their use. However, extrusion of plastic pipe, such as PVC (polyvinyl chloride) pipe has been limited by diameter and weight, thus preventing competition with conventional concrete pipe for large-diameter sewer applications. However, relatively recent advances in technology have enabled production of heavy-duty PVC pipe in bores up to 60 inches and larger, which is large enough to compete with concrete. For example, a system for producing large-diameter, hollow profile pipe is described in U.S. Pat. Nos. 3,917,500 and 4,033,808 involving spiral winding and infrared welding of an extruded hollow core rectangular profile. The resulting large bore pipe has compressive strength and stiffness of solid-wall pipe at a 50 to 60 percent savings in material.
While this hollow form of pipe has many advantages including production of heavy-duty PVC pipe in very large bores, and in virtually unlimited lengths, a problem encountered with this form of pipe is that the extruded hollow core profile produces channels having a spiral or helical configuration continuously throughout the pipe. If, for example, external liquid gets into this hollow, spiral channel of the pipe, it will eventually get to the inside of the pipe through the spigot end of the pipe, causing a leak if the spigot end is not sealed between its inner and outer walls. Alternatively, internal fluid leaking into the spiral channel could exit the belled end of the pipe, if that end is not sealed between its inner and outer walls. One attempt to solve such problem has been to file down the spigot end and then cover the holes in the ends and sharp edges with epoxy plastic putty. However, this approach is very time consuming and such epoxy resinous-type putty is very expensive. Additionally, in rough field handling, the putty pops out of the holes upon impact of the pipe.
U.S. Pat. Nos. 4,390,383, 4,280,534 and 4,341,392 disclose sealing end walls of hollow plastic pipes having lengthwise extending channels by heating and bending the ends to fuse sealing closed. U.S. Pat. No. 3,464,450 discloses the use of seal-type members in the form of a circular flange having projections with a helical outline whose pitch is the same as that of the ribs. However, none of these patents address impact resistance problems of the pipe ends.